[PATCH] tree-optimization/99947 - avoid v.safe_push (v[0])

[Richard Biener]

This avoids (again) the C++ pitfall of pushing a reference to
sth being reallocated.

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

2021-04-07  Richard Biener  <rguent...@suse.de>

        PR tree-optimization/99947
        * tree-vect-loop.c (vectorizable_induction): Pre-allocate
        steps vector to avoid pushing elements from the reallocated
        vector.

        * gcc.dg/torture/pr99947.c: New testcase.
---
 gcc/testsuite/gcc.dg/torture/pr99947.c | 18 ++++++++++++++++++
 gcc/tree-vect-loop.c                   |  3 ++-
 2 files changed, 20 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.dg/torture/pr99947.c

diff --git a/gcc/testsuite/gcc.dg/torture/pr99947.c 
b/gcc/testsuite/gcc.dg/torture/pr99947.c
new file mode 100644
index 00000000000..2cf3ec6aeb8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/torture/pr99947.c
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+
+int a, b, d, e;
+short c;
+void f() {
+  for (; e; e++) {
+    int g = 6;
+    for (; g > 2; g--) {
+      int i = -8;
+      while (i < 20) {
+        i += 5;
+        a += b;
+      }
+      c *= d;
+    }
+    b--;
+  }
+}
diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
index 4e928c65b31..93fa2928e00 100644
--- a/gcc/tree-vect-loop.c
+++ b/gcc/tree-vect-loop.c
@@ -8202,11 +8202,12 @@ vectorizable_induction (loop_vec_info loop_vinfo,
          /* Fill up to the number of vectors we need for the whole group.  */
          nivs = least_common_multiple (group_size,
                                        const_nunits) / const_nunits;
+         vec_steps.reserve (nivs-ivn);
          for (; ivn < nivs; ++ivn)
            {
              SLP_TREE_VEC_STMTS (slp_node)
                .quick_push (SLP_TREE_VEC_STMTS (slp_node)[0]);
-             vec_steps.safe_push (vec_steps[0]);
+             vec_steps.quick_push (vec_steps[0]);
            }
        }
 
-- 
2.26.2